System and method for waste heat utilization in carbon dioxide capture systems in power plants

ABSTRACT

Disclosed herein is a system comprising an absorber; the absorber permitting contact between a flue gas stream that comprises carbon dioxide and a solvent to produce a carbon dioxide rich solvent; a regenerator disposed downstream of the absorber; the regenerator being operative to dissociate the carbon dioxide from the solvent; and a compression system disposed downstream of the regenerator comprising a plurality of compression stages; where each compression stage comprises a compressor that is operative to pressurize the carbon dioxide that is dissociated from the solvent; and where at least some of the compression stages comprise a knockout tank disposed upstream of the compressor and an intercooling heat exchanger disposed downstream of the compressor; where the knockout tank is operative to remove liquid present in the carbon dioxide and where the intercooling heat exchanger is operative to remove heat generated during the pressurizing of the carbon.

TECHNICAL FIELD

This disclosure relates to a system and to a method for capturing wasteheat in a carbon dioxide capture system in a power plant. In particular,this disclosure relates to a system and to a method for capturing wasteheat in a carbon dioxide capture system in a power plant without anymodifications to the stripper or to the reboiler.

BACKGROUND

In the combustion of a fuel (e.g., coal, oil, peat, waste, biofuel,natural gas, or the like used for the generation of power or for theproduction of materials such as cement, steel or glass, or the like, astream of hot flue gas (also sometimes known as process gas) isgenerated. Such a hot flue gas contains, among other components, carbondioxide (CO2).

The negative environmental effects of releasing carbon dioxide to theatmosphere have been recognized, and have resulted in the development ofprocesses adapted for removing or reducing the amount of carbon dioxidefrom the flue gas streams. Solvents can efficiently remove carbondioxide as well as other contaminants, such as sulfur dioxide andhydrogen chloride, from a flue gas stream.

A typical system for treating solvents comprises an absorber, a solventstripper (hereinafter termed “regenerator”), and a compression systemthat is operative to pressurize the carbon dioxide. While the solvent isgenerally an amine, other solvents can also be used (e.g., methanol,ethanol, ammonia, water, or mixtures thereof). FIG. 1 is a prior artdepiction of a system 100 for removing carbon dioxide from a flue gasstream by utilizing solvents (e.g., aqueous amine solution as just oneof the other possibilities). The system 100 comprises an absorber 102; aregenerator 104; a partial condenser 106; a reboiler 118; and acompression system 110 that comprises at least a compressor 114, aknockout tank 112, and a heat exchanger 116.

A flue gas stream 101 comprising carbon dioxide emanating from a sourceof combustion (e.g., a power plant) is directed to an absorber 102 whereit is contacted with a solvent (e.g., aqueous amine solution—hereinaftersolvent) stream 111. The solvent absorbs carbon dioxide from the fluegas stream to form a carbon dioxide rich solvent stream 103 (hereinafter“rich solvent stream”). A treated flue gas stream that is free orpartially free from carbon dioxide is discharged from the absorber 102usually to atmosphere via a stack and/or via other pieces of equipmentsuch as heat exchangers, filters, and the like. As shown in the FIG. 1,the carbon dioxide rich solvent stream 103 is directed to a regenerator104, where the carbon dioxide gas is released either completely orpartially from the solvent. Two streams emanate from the regenerator104—a carbon dioxide rich stream 107 and a lean solvent stream 111 thatcontains the solvent and byproducts of the solvent and unreleased carbondioxide. The carbon dioxide rich stream 107 emanating from theregenerator 104 is compressed to a high pressure in the compressionsystem 110.

In the compression system 110, the carbon dioxide rich stream 107 isfirst fed to the knock out tank 112, where any liquids present areremoved (this liquid can be water from any aqueous solution used assolvent or can be flue gas moisture). The vapors and solvents arecondensed and removed from the bottom of the knock out tank 112. Thecarbon dioxide stream emanating from the top of the knock out tank 112is fed to a compressor 114, where it is compressed to a high pressurefor purposes of sequestering the carbon dioxide and/or enhanced oilrecovery (EOR) and/or carbon dioxide capture and utilization (CCU)and/or other purposes.

During the compression in the compressor 114, the temperature of thecarbon dioxide increases. The hot carbon dioxide stream 121 is thendischarged to a heat exchanger 116, which extracts heat from the hotcarbon dioxide gas thus cooling it. The carbon dioxide is thendischarged from the heat exchanger 116 to a pipeline for sequestrationand/or enhanced oil recovery (EOR) and/or carbon dioxide capture andutilization (CCU) and/or other purposes. The heat exchanger 116 iscooled by cooling water.

The regenerator 104 is in fluid communication with a partial condenser106 and a reboiler 118. The partial condenser 106 functions to removevaporized solvent and/or vaporized solvent components contained in thecarbon dioxide stream emitting from the top of the regenerator 104partially or almost completely. The partial condenser 106 receivescooling water (cold) from a cooling water supply to condense vaporscontained in the carbon dioxide stream emitting from the top of theregenerator 104.Warm water from the partial condenser 106 is thendischarged to a cooling tower (not shown) and/or any other heat sinke.g. air cooled heat exchanger. The solvent and/or solvent componentsremoved in the partial condenser is then discharged back into theregenerator 104.

The reboiler 118 is operative to heat up the solvent at the regeneratorbottom. Therefore it uses heating steam from the power plant steamcycle. Condensate from the reboiler 118 is then discharged back to thepower plant steam cycle. A solvent stream 111 collected in the reboileris recycled to the top of the absorber 102 via a heat exchanger 120.Heat is transferred to the carbon rich solvent stream 103 from thesolvent stream 111 in the heat exchanger 120.

It is generally desirable to reuse heat generated in the compressor 114.Improving heat utilization generated during compression is thereforedesired. Previous attempts to achieve this have involved redesigning thereboiler or the regenerator. Attempts to redesign the reboiler or theregenerator have proven to be expensive, disturb chemical equilibrium inthe regenerator and require additional maintenance of the system 100.For example, regenerator columns are modified by partially integratingcompression into the regenerator to recover waste heat. This is notshown in the FIG. 1. Since the compression is partially integrated intothe regenerator columns, the pressure of the released carbon dioxide isincreased which affects the chemical equilibrium and hence might requirethe regenerator vessel (104) redesign.

It is therefore desirable to redesign the compression system forefficient utilization of heat generated during compression while notchanging either the structure of the reboiler and/or that of thestripper. It is also desirable to redesign the compression system sothat it can be used in either a new plant or as a retrofit.

SUMMARY

Disclosed herein is a system comprising an absorber; the absorberpermitting contact between a flue gas stream that comprises carbondioxide and a solvent to produce a carbon dioxide rich solvent; aregenerator disposed downstream of the absorber; the regenerator beingoperative to dissociate the carbon dioxide from the solvent; and acompression system disposed downstream of the regenerator comprising aplurality of compression stages; where each compression stage comprisesa compressor that is operative to pressurize the carbon dioxide that isdissociated from the solvent; and where at least some of the compressionstages comprise a knockout tank disposed upstream of the compressor andan intercooling heat exchanger disposed downstream of the compressor;where the knockout tank is operative to remove liquids present in thecarbon dioxide and where the intercooling heat exchanger is operative toremove heat generated during the pressurization of the carbon dioxide.

Disclosed herein too is a method comprising discharging a carbon dioxidestream into a compression system; pressurizing the carbon dioxide streamin the compression system; where the compression system comprises aplurality of compression stages; where each compression stage comprisesa compressor that is operative to pressurize the carbon dioxide that isdissociated from the solvent; and where at least some of the compressionstages comprise a knockout tank disposed upstream of the compressor andan intercooling heat exchanger disposed downstream of the compressor;where the knockout tank is operative to remove liquid (condensed)solvent and/or solvent components like water present in the carbondioxide and where the intercooling heat exchanger is operative to removeheat generated during the pressurizing of the carbon dioxide; removingresidual liquid (condensed) solvent and/or solvent components like waterin the knockout tank; cooling compressed carbon dioxide in theintercooling heat exchanger with a coolant which may be water amongother possibilities; and discharging the pressurized carbon dioxide to asequestration station and/or enhanced oil recovery (EOR) and/or carbondioxide capture and utilization (CCU) and/or other purposes.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a prior art depiction of a system for removing carbon dioxidefrom a flue gas stream by utilizing a solvent (e.g., an aqueous aminesolution);

FIG. 2 depicts an exemplary system for compressing carbon dioxide usingmultistage compression;

FIG. 3 depicts another exemplary system for compressing carbon dioxideusing multistage compression; and

FIG. 4 depicts an exemplary system for recovering heat from thecompressed carbon dioxide by heat exchangers and reusing the heat in theregenerator.

DETAILED DESCRIPTION

Disclosed herein is a system for the compression of carbon dioxide priorto sequestration. The system advantageously comprises a compressionsystem that comprises a plurality of compressor stages disposeddownstream of a regenerator and upstream of a sequestration station. Theplurality of compressors are used for sequentially compressing thecarbon dioxide to a pressure desired for sequestration and/or enhancedoil recovery (EOR) and/or carbon dioxide capture and utilization (CCU)and/or other purposes. The heat generated during this compression isabsorbed by cooling water in intercoolers or in an after-cooler.

The use of multistage compression is advantageous in that it permitsenergy savings in the form of efficient and improved power consumption.The demand for compression power (electricity) is reduced. The systemdisclosed herein does not require any modification of absorbers,regenerators or reboilers and can therefore be used in a new power plantsystem or advantageously in an existing power plant as a retrofit.

Disclosed herein too is a method comprising multiple compression stagesarranged in series where carbon dioxide gas (removed from a flue gasstream) is successively compressed to a desired pressure forsequestration. Each compression stage successively compresses the carbondioxide gas in a compression ratio of about 1.5:1 to 4:1 and dischargesthe compressed carbon dioxide to the next compression stage. Thecompressed carbon dioxide emanating from each compressor is fed to aknockout tank to remove liquid (condensed) solvent and/or solventcomponents like water entrained in the carbon dioxide. One or moreintercoolers located downstream of one or more compressors in thevarious compression stages removes the heat generated during compressionand discharges the cooling water to a mixer from which it is cooled in aheat exchanger and further in an optional cooling tower.

With reference now to the FIG. 2, an exemplary system 200 forefficiently utilizing the heat of compression comprises an absorber 202,a regenerator 204, and a compression system 300 (bounded by dottedlines). The absorber 202 lies upstream of the regenerator 204, which inturn lies upstream of the compression system 300. The compression system300 comprises a plurality of compressor stages with intercooling andafter cooling. The compression system 300 can comprise 2 or morecompression stages, specifically 3 or more compression stages,specifically 4 or more compression stages and more specifically 5 ormore compression stages disposed downstream of the regenerator 204 andupstream of a sequestration station (not shown). In an exemplaryembodiment, a compression system 300 comprising at least 6 or morecompression stages are disposed downstream of the regenerator 204. Theregenerator 204 is also in fluid communication with a first partialcondenser 406 and a reboiler 418. The partial condenser 406 and thereboiler 418 are each in recycle loops with the regenerator 204.

In one embodiment, with reference to the FIG. 2, a flue gas stream 201containing carbon dioxide is discharged into the absorber 202 where itis absorbed by a solvent. The carbon dioxide rich solvent stream 203 isdischarged to the regenerator 204 via a heat exchanger 520 andcompletely or partially (shown in FIG. 2 is the case for the former) thecompression system 300. In the regenerator 204, the solvent is separatedfrom the carbon dioxide gas. The carbon dioxide stream 205 is dischargedto the compression system 300, where it undergoes compression forpurposes of sequestration. This compression in the compression system300 and the return of the solvent to the regenerator will be detailed inthe FIGS. 3 and 4. The solvent stream 411 that is separated from thecarbon dioxide rich solvent stream 203 in the regenerator 204 isrecycled to the absorber 202 via the heat exchanger 520, where itexchanges heat with the carbon dioxide rich solvent stream 203 thatemanates from the absorber 202.

In one embodiment, at least a portion of the compression stagescomprises a knockout tank, a compressor and an intercooling heatexchanger. The knockout tank lies upstream of the compressor, which liesupstream of the intercooling heat exchanger. In each stage, the knockouttank lies upstream of the respective compressor, while the intercoolingheat exchanger lies downstream of the respective compressor. In anexemplary embodiment, for a compression system comprising at least 6compression stages, at least 4 compression stages comprise anintercooling heat exchanger disposed downstream of the respectivecompressor, while one stage comprises an after cooling heat exchangerdisposed downstream of the respective compressor.

In an exemplary embodiment, depicted in the FIG. 3, the firstcompression stage of the compression system 300 comprises a firstknockout tank 206, a first compressor 208, an a first intercooling heatexchanger 210 that lie downstream of the regenerator 204; the secondcompression stage comprises a second knockout tank 212, a secondcompressor 214 and a second intercooling heat exchanger 216 that liesdownstream of the first compression stage; the third compression stagecomprises a third knockout tank 218, a third compressor 220 and a thirdintercooling heat exchanger 222 that lies downstream of the secondcompression stage, and the fourth compression stage comprises a fourthknockout tank 224, a fourth compressor 226, and a fourth intercoolingheat exchanger 228 that lies downstream of the third compression stage.The fifth compression stage comprises an absorber 230 for absorbingresidual water present in the carbon dioxide and a fifth compressor 226,with the absorber 230 being disposed downstream of the compressor 226.The fifth compression stage lies downstream of the fourth compressionstage. The sixth compression stage lies downstream of the fifthcompression stage and comprises a sixth compressor 234 and a firstafter-cooling heat exchanger 236. The after-cooling heat exchanger liesdownstream of the sixth compressor 234, which in this exemplaryembodiment is the final compressor. The sixth compressor 234 liesupstream of the first after-cooling heat exchanger 236. The compressors208, 214, 220, 226, 232 and 234 are in mechanical communication with atleast a driver (i.e. motor) 242. The motor 242 does mechanical work indriving the compressors to compress the carbon dioxide to the desiredpressure for sequestration.

In the first stage of compression, a carbon dioxide stream 205 emanatingfrom the regenerator 204 at a temperature T1 and a pressure P1 isdischarged to the first knockout tank 206, where solvent and/or solventcomponents like water moisture entrained in the carbon dioxide stream205 is flashed off The carbon dioxide stream 207 emanating from theknockout tank 206 at a temperature T2 and pressure P2 is then dischargedto the compressor 208 where it is compressed. At this stage T2 isgreater than T1 and P2 is greater than P1. The compressed carbon dioxidestream 209 is then discharged to the first intercooling heat exchanger210 where it is cooled down by exchanging its heat with cooling water.

In the second stage of compression, the carbon dioxide stream 229emanating from the second intercooling heat exchanger 210 is dischargedto a second knock out tank 212 where additional liquid (e.g., condensedsolvent and/or moisture from flue gases) is removed. The carbon dioxidestream 211 now at a temperature T3 and pressure P3 is then compressed inthe second compressor 214 to a temperature T4 and pressure P4 prior tobeing discharged via stream 213 to the second intercooling heatexchanger 216 where it is subjected to cooling with cooling water.

In the third stage of compression, the carbon dioxide stream 231emanating from the third intercooling heat exchanger 216 is dischargedto a third knock out tank 218 where additional liquid (e.g., condensedsolvent and/or moisture from flue gases) is removed. The carbon dioxidestream 215 now at a temperature T5 and pressure P5 is then compressed inthe third compressor 220 to a temperature T5 and pressure P6 prior tobeing discharged via stream 217 to the third intercooling heat exchanger222 where it is subjected to cooling with cooling water.

In the fourth stage of compression, the carbon dioxide stream 233emanating from the third intercooling heat exchanger 222 is dischargedto a fourth knock out tank 224 where additional liquid (e.g., condensedsolvent and/or moisture from flue gases) is removed. The carbon dioxidestream 219 now at a temperature T7 and pressure P7 is then compressed inthe fourth compressor 226 to a temperature T8 and pressure P8 prior tobeing discharged via stream 221 to the fourth intercooling heatexchanger 228 where it is subjected to cooling with cooling water.

After the fourth compression stage the carbon dioxide stream is directedto an absorber 230 (e.g., a moisture removal system) comprising adesiccant to remove liquid (e.g., moisture from solvents and/or water).Depending on the process conditions and selected type of the moistureremoval system, the moisture removal system can be at the downstream ofany compressor in the compression system 300. Shown in FIG. 3 is just aselected case where the moisture removal system is at the downstream ofthe fourth compression stage. The carbon dioxide stream 239 at apressure P9 and temperature T9 is then directed to the fifth compressor232 (the fifth compression stage) where it is compressed further anddirected to the sixth compressor 234 (the sixth compression stage) whereit is further compressed to a temperature T10 and pressure P10. Afterthe sixth compression stage, the carbon dioxide stream 241 is dischargedto the first after cooler 236 where it is cooled down to a pressure P11and temperature T11. The pressure P11 and the temperature T11 is thepressure and temperature at which the carbon dioxide stream issequestered and after the first after cooler 236, the carbon dioxidestream 243 is sequestered.

The liquid (e.g., condensed solvent and/or moisture from flue gases) isseparated out in each of the knockout tanks is collected in a singleknockout tank and is then discharged. In one embodiment, the liquidcollected in the fourth knockout tank 224 is discharged to the thirdknockout tank 218 where it is combined with liquid from the thirdknockout tank 218 and from which it is discharged to the second knockouttank 212 (to be combined with liquid present in the second knockouttank) and then discharged to the first knockout tank 206. All of theliquid is collected in the first knockout tank 206 and then dischargedto the exterior.

Cooling water used in the first after-cooling heat exchanger 236, thefourth intercooling heat exchanger 228, the third intercooling heatexchanger 222, the second intercooling heat exchanger 216 and the firstintercooling heat exchanger 210 is discharged to a mixer 238 where it ismixed and then discharged to a heat exchanger 240, where it is cooled toa desired temperature before being discharged to a cooling tower (notshown). Alternatively, the water may be discharged directly to a coolingtower after being mixed in the mixer 238.

In each compression stage the carbon dioxide stream emanating from theregenerator 204, has liquid extracted from it in the knockout tankfollowing which the carbon dioxide stream is compressed in thecompressor to a ratio of about 1.5:1 to about 4:1, about 1.5:1 to about4:1, specifically about 1.6:1 to about 3:1, and more specifically about1.7:1 to about 2.5:1 in the first compressor 208. In an exemplaryembodiment, the first compressor 208 compresses the carbon dioxidestream in an amount of about 2:1.

In an exemplary embodiment, the temperature in each compression stage isincreased by a factor of about 1.5 to about 3.5, specifically about 1.75to about 3.0, and more specifically 2.0 to about 2.75 from thetemperature of the carbon dioxide stream prior to entering the firstcompressor. The compressed carbon dioxide, now at a higher pressure andtemperature (than it was prior to the compression in each compressor) isthen discharged from the compressor to the intercooling heat exchangerif desired in order to exchange heat with coolant (i.e. cooling water orany other cooling material). The cooling water heated up in theintercooling heat exchanger is discharged to a cooling tower forcooling. The temperature of the cooling water is generally increased byabout 5 to about 15° C., specifically about 7 to about 12° C. in eachintercooling heat exchanger as the water absorbs heat from thecompressed carbon dioxide. In extreme cases, the temperature of thecooling water can be increased by up to 50° C.

As detailed briefly above, in one manner of operating the system 200 ofthe FIG. 2, a flue gas stream 201 is contacted with a solvent to form acarbon dioxide rich solvent stream 203, which is then discharged to theregenerator 204. Carbon dioxide gas released from the solvent is thendischarged and subjected to compression in the plurality of compressionstages depicted in the FIGS. 2, 3 and 4.

The carbon dioxide gas stream 205 is first discharged from theregenerator 204 to the knockout tank 206 (see FIG. 3), where some of themoisture contained in the carbon dioxide gas stream is collected. Thecarbon dioxide gas stream 207 emanating from the first knock out tank206 is then compressed in the first compressor 208 to a compressionratio of about 1.5:1 to about 4:1. In an exemplary embodiment, the firstcompressor 208 compresses the carbon dioxide stream in an amount ofabout 2:1.

The temperature of the carbon dioxide stream 209 exiting the firstcompressor is increased by a factor of about 2.0 to about 2.5 from thetemperature of the carbon dioxide stream 207 prior to entering the firstcompressor 208. In a exemplary embodiment, the temperature T1 andpressure P1 of the carbon dioxide stream 207 prior to being compressedin the first compressor 208 is about 40° C. and about 3.0 bar (3.05kilograms per square centimeter) respectively, while the temperature T2and pressure P2 after compression is about 112° C. and 6.2 bar (6.10kilograms per square centimeter) respectively.

The compressed carbon dioxide stream 209 is then discharged to the firstintercooling heat exchanger 210, where the heat of compression isabsorbed by cooling water. The temperature of the cooling water isincreased by about 5 to about 15° C., specifically about 7 to about 12°C. in the intercooling heat exchanger 210 as it absorbs heat from thecompressed carbon dioxide. In an exemplary embodiment, the cooling waterfrom the intercooling heat exchanger 210 is then discharged to a mixer238, from which it is discharged to a heat exchanger 240 where it iscooled from about 23.1° C. to about 13.1° C.

In an exemplary embodiment, the temperature T3 and pressure P3 of thecarbon dioxide stream 211 after the second knockout tank 212 and priorto entering the second compressor is 39.5° C. and 5.9 bar (6.0 kilogramsper square centimeters

In summary, the temperature of the carbon dioxide stream after eachstage of compression increases by a factor of about 2.0 to about 2.5from the temperature of the carbon dioxide stream prior to compression.After being discharged to the respective knockout tanks in each stage ofcompression, the temperature of the carbon dioxide stream issubstantially similar to the temperature of the carbon dioxide streamprior to undergoing compression.

In this manner, in a compression system comprising multiple stages ofcompression, the temperature of the carbon dioxide stream prior to eachcompression stage is almost identical to each other. For example withreference to the FIG. 3, T1≈T3≈T5≈T7 (where the symbol “≈” meansapproximately) and so one. In a similar manner, the temperature of thecarbon dioxide stream after each compressions stage is almost identicalto each other. For example with reference to the FIG. 3, T2≈T4≈T6≈T8 andso one. In one embodiment, there may be a slight decrease in thetemperature of the carbon dioxide stream after each successivecompression stage. Thus for example, T2 may be slightly greater than T4,which is slightly greater than T6, which is slightly greater than T8.

With regard to the pressure in each compression stage, the process ofthe first compression stage is repeated through the second compressionstage, the third compression stage, the fourth compression stage, and soon. At each stage, the respective compressors 214, 220 and 226 subjectthe carbon dioxide gas to a compression ratio of about 1.5:1 to about4:1, specifically about 1.6:1 to about 3:1, and more specifically about1.7:1 to about 2.5:1 and most specifically about 2:1. Thus if thepressure of the carbon dioxide stream prior to the first compressionstage is P1, the pressure prior to the second stage of compressionP3≈2P1, while the pressure prior the third stage of compressionP5≈2P3≈4P1, while the pressure prior the fourth stage of compression isP4≈2P3≈4P2≈8P1.

The fifth compression stage comprises a compressor 232, but does notcontain a knockout tank or an intercooling heat exchanger. Instead afterthe fourth compression stage, the carbon dioxide gas stream isdischarged to an absorber 230 that comprises a desiccant that absorbsthe remaining water present in the carbon dioxide. An exemplarydesiccant is triethylene glycol (TEG).

The carbon dioxide gas stream now devoid of moisture is discharged tothe fifth compressor 232 and then to the sixth compressor 234. In thefifth and the sixth compressors, the carbon dioxide gas stream is onceagain pressurized to a compression ratio of about 1.5:1 to about 4:1 ineach compressor, while the temperature is increased from about T1 priorto the fifth compressor to a temperature T5 of about 1.8 to about 2.0 T1after compression in the fifth compressor 232. The pressure prior thesixth stage of compression is P9≈32P1.

After the sixth compressor, the temperature T10 is increased to about3.5 to about 4.0 T1, while the pressure P10 is about 35P1 to about 40P1.In an exemplary embodiment, the pressure of the carbon dioxide streamafter compression in the sixth compression stage is about 110 bar (about112 kilograms per square centimeters), which is the pressure desired forcarbon dioxide sequestration. The carbon dioxide stream aftercompression in the sixth compression stage is then discharged to thefirst after-cooling heat exchanger 236, where it is pressure is about110 bar (about 112 kilograms per square centimeters). The temperature ofthe carbon dioxide stream after the fifth intercooler 236 is about 45 toabout 55° C., specifically about 50° C.

The cooling water used in the respective intercoolers at eachcompression stage is mixed in a mixer and is discharged to a heatexchanger 240 at a temperature of about 20 to about 25° C., specificallyabout 23° C., while after the heat exchanger 240, the temperature of thecooling water is about 10 to about 15° C., specifically about 13° C. Theheat exchanger 240 receives cooling water from a cooling tower or anyother cooling water device. In a similar manner, the heat exchangers210, 216, 222, 228 and 236 can receive cooling water from the coolingtower, any other cooling water device. The cooling fluid can be obtainedfrom any other heat exchanger as well.

Table 1 depicts the temperatures and pressures at points A1 through A11for /the FIG. 3, where A1 refers to point at which the temperature T1and the pressure P1 are measured, A2 refers to point at which thetemperature T2 and the pressure P2 are measured, A3 refers to point atwhich the temperature T3 and the pressure P3 are measured, and so on.

TABLE 1 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 T (° C.) 39.2 111.9 39.5108.3 39.7 103.1 39.7 98.1 99.7 150.3 49 P (bar) 2.9 6.2 5.9 11.9 11.622.1 21.8 39.1 70.2 110.5 110.2

In one embodiment, with reference to the set-up in the FIG. 4, theelectrical load on the compressor is about 22,000 to about 30,000kilowatts, specifically about 25,000 to about 28,000 kilowatts. The heatrecovered from the intercooling heat exchangers is about 20,000 to about40,000 kilowatts, specifically about 37,000 to about 39,000 kilowatts.

In another exemplary embodiment, depicted in the FIG. 4, theintercooling heat exchangers of one or more compression stages can beremoved from the system depicted in the FIG. 3. In another embodiment,some of the knockout tanks can be removed from the compression stageimmediately following the compression stage where the intercooler hasbeen removed. When an intercooling heat exchanger of a particularcompression stage is removed, it may be replaced by an additional heatexchanger added downstream of the succeeding compression stage fromwhere the intercooler has been removed.

For example, an intercooler removed in the first compression stage maybe replaced by a heat exchanger located downstream of the compressor inthe second stage. Thus the removal of three intercooling heat exchangersfrom various compression stages results in the utilization of at leastthree heat exchangers in the succeeding compression stages. In oneexemplary embodiment, the heat exchangers can be used to remove carbondioxide from the carbon dioxide rich solvent, thus saving energy that isused in the regenerator 204. This is depicted by stream 502 in the FIG.4. This set-up can reduce the steam used in the reboiler (not shown).Depending upon the pressure level of the extracted steam, this can saveelectrical energy in an amount of about 4 to 4.4 megawatts if the savedlow pressure steam is expanded in a steam turbine. This method isadvantageous in that the power consumption is increased by about 5 toabout 10%, specifically about 7 to about 9%. The cooling water demand isreduced by about 35 to about 45%, specifically about 36 to about 40%.The heat utilization by the regenerator column is increased in an amountby up to about 40%, specifically about 5 to about 37%.

With reference now to the FIG. 4, the carbon dioxide stream 207emanating from the knockout chamber 206 at a temperature and pressure atpoint (Al) indicated by (T1, P1) is discharged to the first compressor208 where it is compressed to A2(T2, P2). Here A2 refers to the pointwhere T2 and P2 are measured in the FIG. 3. It is then directlydischarged to the second compressor 214 where it is subjected toadditional compression to reach temperature and pressure A3(T3, P3).After compression, the carbon dioxide stream is discharged to a firstheat exchanger 306 and then to the first intercooling heat exchanger 216and the first knockout tank 218. The carbon dioxide stream now at A4(T4,P4) is then discharged to the third compressor 220 to reach temperatureand pressure A5(T5, P5) and to the fourth compressor 226 to reachtemperature and pressure A6(T6, P6). After the fourth compressor thecarbon dioxide stream is discharged to the second heat exchanger 304 andthen to second intercooling heat exchanger 228 and then to absorber 230where any residual water is removed. The carbon dioxide stream at A7(T7,P7) is then discharged to the fifth compressor 232 to reach temperatureand pressure A8(T8, P8) and the sixth compressor 234 to reachtemperature and pressure A9(T9, P9). After the sixth compressor 234 thecarbon dioxide stream is discharged to the third heat exchanger 302 andthen to the third intercooling heat exchanger 236 from which it isdischarged to the sequestration station (not shown) at a temperature andpressure of A10(T10, P10).

In one embodiment, the water stream 502 used in the heat exchangers 302,304 and 306 (to recover heat from the compressed carbon dioxide) canhave heat recovered from them in a heat recovery steam generator. Inanother embodiment, the heat recovered from the heat exchangers 302, 304and 306 is used in the regenerator to supply up to 16 megawatts ofenergy to the regenerator.

The Table 2 shows the various temperatures and pressures at the variouspoints A1 to A10 for a system having 6 compression stages with 2intercooling heat exchangers, 1 after-cooling heat exchanger and the 3heat exchangers as depicted in the FIG. 4.

TABLE 2 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 T (° C.) 39.2 111.9 184.7 39.7105.8 170.1 39.7 100.5 151.6 49 P (bar) 2.9 6.2 11.3 11.3 22.1 39.1 38.570.2 110.8 110.2

In the system depicted in the FIG. 4, the temperature prior tocompression in each odd numbered compressor is substantially the same.Thus, for example, T1≈T4≈T7. The temperature after compression at stagesA3, A6, A8 and A9 is substantially elevated when compared with thetemperatures prior to compression. The compression at each stagecompresses the carbon dioxide in a compression ratio of about 1.5:1 toabout 4:1, specifically about 1.6:1 to about 3:1, and more specificallyabout 1.7:1 to about 2.5:1 and most specifically about 2:1. The pressureduring the 6 stages of compression shown in the Table 2 follows thatpattern reflected in the Table 1 (which represents data from the FIG.1).

In one embodiment, with reference to the set-up in the FIG. 4, theelectrical load on the compressor is about 22,000 to about 30,000kilowatts, specifically about 25,000 to about 28,000 kilowatts. The heatrecovered from the intercooling heat exchangers is about 20,000 to about40,000 kilowatts, specifically about 22,000 to about 26,000 kilowatts.

In this embodiment, the heat recovered from the compression of thecarbon dioxide is used to recover the carbon dioxide from the solvent.The reutilization of heat in this manner increases the power plantefficiency by up to about 2 percentage points. In an exemplaryembodiment, the reutilization of heat in this manner increases theefficiency of the power plant by up to one percentage point. Thisreutilization of heat in the heat exchangers 302, 304, and 306 resultsin a reduction of the reboiler duty by an amount of up to 8%,specifically about 5% to about 7%.

The cooling water demand is reduced by up to 27%, specifically about 15to about 25% by the use of the three heat exchangers 302, 304 and 306.In addition, there is a potential for using a smaller reboiler when theheat recovered from water is used in the regenerator. In addition, anyadditional power used in the multistage compression can be compensatedfor by a reduction in reboiler steam demand.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein,singular forms like “a,” or “an” and “the” are intended to include theplural forms as well, unless the context clearly indicates otherwise. Itwill be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother elements as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not be/construed as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

The term and/or is used herein to mean both “and” as well as “or”. Forexample, “A and/or B” is construed to mean A, B or A and B.

The transition term “comprising” is inclusive of the transition terms“consisting essentially of and “consisting of and can be interchangedfor “comprising”.

While this disclosure describes exemplary embodiments, it will beunderstood by those skilled in the art that various changes can be madeand equivalents can be substituted for elements thereof withoutdeparting from the scope of the disclosed embodiments. In addition, manymodifications can be made to adapt a particular situation or material tothe teachings of this disclosure without departing from the essentialscope thereof Therefore, it is intended that this disclosure not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this disclosure.

What is claimed is:
 1. A system comprising: an absorber; the absorberpermitting contact between a flue gas stream that comprises carbondioxide and a solvent to produce a carbon dioxide rich solvent; aregenerator disposed downstream of the absorber; the regenerator beingoperative to dissociate the carbon dioxide from the solvent; and acompression system disposed downstream of the regenerator comprising: aplurality of compression stages; where each compression stage comprisesa compressor that is operative to pressurize the carbon dioxide that isdissociated from the solvent; and where at least some of the compressionstages comprise a knockout tank disposed upstream of the compressor andan intercooling heat exchanger disposed downstream of the compressor;where the knockout tank is operative to remove liquid present in thecarbon dioxide and where the intercooling heat exchanger is operative toremove heat generated during the pressurizing of the carbon dioxide. 2.The system of claim 1, where each compression stage comprises theknockout tank and the intercooling heat exchanger.
 3. The system ofclaim 2, where the compression system comprises at least two compressionstages that comprise the knockout tank and the intercooling heatexchanger.
 4. The system of claim 2, where the compression systemcomprises at least four compression stages that comprise the knockouttank and the intercooling heat exchanger.
 5. The system of claim 2,where the compression system further comprises a heat exchanger disposeddownstream of the compressor and upstream of the intercooling heatexchanger.
 6. The system of claim 1, where the intercooling heatexchanger lies downstream of a first compressor and upstream of a secondcompressor.
 7. The system of claim 1, where at least one compressionstage comprises an after-cooling heat exchanger; where the after-coolingheat exchanger lies downstream of a final compressor.
 8. The system ofclaim 1, where cooling water from a plurality of intercooling heatexchangers is discharged to a mixer prior to being discharged to a heatexchanger.
 9. The system of claim 1, where at least one compressionstage comprises an absorber containing a desiccant.
 10. The system ofclaim 5, where a heat transferring fluid from the heat exchanger isdischarged to the regenerator; where the heat transferring fluid hasreceived heat from the pressurized carbon dioxide.
 11. A methodcomprising: discharging a carbon dioxide stream into a compressionsystem; pressurizing the carbon dioxide stream in the compressionsystem; where the compression system comprises: a plurality ofcompression stages; where each compression stage comprises a compressorthat is operative to pressurize the carbon dioxide that is dissociatedfrom the solvent; and where at least some of the compression stagescomprise a knockout tank disposed upstream of the compressor and anintercooling heat exchanger disposed downstream of the compressor; wherethe knockout tank is operative to remove liquid present in the carbondioxide and where the intercooling heat exchanger is operative to removeheat generated during the pressurizing of the carbon dioxide; removingresidual liquid in the knockout tank; cooling compressed carbon dioxidein the intercooling heat exchanger with water; and discharging thepressurized carbon dioxide to a sequestration station.
 12. The method ofclaim 11, further comprising additionally cooling the compressed carbondioxide in a heat exchanger disposed downstream of the compressor andupstream of the intercooling heat exchanger.
 13. The method of claim 12,where the additional cooling occurs in a plurality of heat exchangerseach of which is disposed downstream of a compressor and upstream of anintercooling heat exchanger.
 14. The method of claim 12, where the heatexchanger is cooled with solvent that is used in a regenerator.
 15. Themethod of claim 11, where a heat transferring fluid used in theintercooling heat exchanger is discharged to a mixer and then dischargedto a heat exchanger.